~Topo_Cart();
Topo_Cart(MPI_Comm comm_old, int ndims, int dims[], int periods[], int reorder, MPI_Comm *comm_cart);
Topo_Cart* sub(const int remain_dims[], MPI_Comm *newcomm) ;
~Topo_Cart();
Topo_Cart(MPI_Comm comm_old, int ndims, int dims[], int periods[], int reorder, MPI_Comm *comm_cart);
Topo_Cart* sub(const int remain_dims[], MPI_Comm *newcomm) ;